Agriculture Reference
In-Depth Information
east with increasing summer rainfall (Cowling
1983a
). Geophytes are common
and diverse with many species endemic to renosterveld (Proches
et al.
2006
).
Diversity patterns are poorly known but high alpha diversity has been reported
in western regions, with lower diversity and less turnover of shrub species in
eastern communities (see
Chapter 11
).
Renosterveld is poorly studied relative to fynbos. The vegetation has been
highly fragmented by agriculture (> 90% transformed in the Cape region) with
the most extensive remnants on steep mountain slopes (Kemper
et al.
2000
).
Large areas of renosterveld, especially in the east, may have been grasslands
with
Elytropappus rhinocerotis
invading depending on grazing and fire history.
The shrubland has been converted to C
4
grasslands in southern and eastern
examples by frequent burning to promote grazing (Cowling
et al.
1986
). Similar
human-caused type conversion has occurred in parts of the Cape region as well
(Kraaij
2010
).
The fire ecology of renosterveld is poorly known. The vegetation supports
crown fires at intervals of several decades, with median frequencies longer than
fynbos in the southern Cape (20-30 yrs; Seydack
et al.
2007
). Cape region
renosterveld, unlike many fynbos communities, resembles California sage scrub
in that the fuel is made up of a continuous shrub layer with a discontinuous
graminoid layer, and similar low fuel loads (see
Table 2.1
).
Elytropappus
, the dominant shrub, has a finely branched canopy with very small
cupressoid leaves. It accumulates dead branches and is highly flammable. Indeed
the flammable properties of this single species may account for why renosterveld
replaces succulent Karoo vegetation over much of its range - a plausible example
of
niche construction
by evolution of flammability in a single species (Bond &
Midgley
1995
; Kerr
et al.
1999
).
Elytropappus
is usually killed by fires, though
some resprouting populations are known from the eastern parts of its range.
Recruitment is fire stimulated with shade-intolerant seedlings (Levyns
1929
). As
in fynbos, the large broadleaf shrubs in renosterveld become more prominent in
thicket formations and all are obligate resprouters (Taylor
1978
). The fire
responses of other shrubs seem to vary along geographic gradients with fire-
stimulated obligate seeders in mountain renosterveld in the Western Cape (e.g.
Aspalathus
spp.), but mostly resprouting members of the Asteraceae (
Relhania
,
Pteronia
) in the eastern distribution of the formation.
Many of the associated geophytes in renosterveld have fire-stimulated
flowering but there is no information on whether fire is an obligate cue. Fire
ephemerals also occur and some have smoke-stimulated germination (C.J.
Fotheringham personal communication) suggesting that, in at least part of its
range, renosterveld has fire-dependent elements. Despite its aridity relative to
fynbos, the more mesic stands of renosterveld are prone to invasion by
alien trees, usually conifers and acacias. Local patches of broadleaf forest
dominated by
Olea africana
and
Rhus
spp. occur in fire-protected sites, indicat-
ing a potential for shifting to an alternative ecosystem state in the absence of
burning (Boucher & Moll
1981
).
